Method for forming aligned patterns on a substrate

ABSTRACT

A method for forming a second pattern in registration with a first pattern on a substrate is disclosed. The method comprises providing the substrate having a first magnitude of an associated electrical characteristic and at least one alignment structure that is associated with a second magnitude of the electrical characteristic different from the first magnitude. A controller is used to control an electrical probe to measure the electrical characteristic at a plurality of positions proximate the substrate. The measured electrical characteristic corresponds to the alignment structure when the probe is proximate to the alignment structure and to the substrate when the probe is not proximate to the alignment structure. The measured electrical characteristics are used to identify a location of the alignment structure. The second pattern is formed so that it is in registration with the first pattern, based on the identified location of the alignment structure.

CROSS-REFERENCE TO RELATED APPLICATION(S)

Reference is made to commonly-assigned, U.S. patent application Ser. No.14/230,114, entitled “SYSTEM FOR ALIGNING PATTERNS ON A SUBSTRATE”, Ser.No. 14/230,107, entitled “METHOD FOR ALIGNING PATTERNS ON A SUBSTRATE”,Ser. No. 14/230,140, entitled “SYSTEM FOR FORMING ALIGNED PATTERNS ON ASUBSTRATE”, Ser. No. 14/230,153, entitled “ALIGNMENT STRUCTURE FORREGISTERING PATTERNS ON A SUBSTRATE”, all filed Mar. 31, 2014.

TECHNICAL FIELD

The present invention generally relates to registration of a secondpattern with respect to a first pattern, and more particularly to usingan alignment structure having a location identified by electricalmeasurements for the registration.

BACKGROUND

Multi-layer articles, such as multi-layer devices or multi-layercircuits, are typically made as a plurality of layers that are formed insequence. Multi-layer articles can be made by successive forming ofpatterned layers on a single substrate, either on one side or on twoopposite sides of the substrate. Alternatively, the patterned layers canbe formed on a plurality of substrates, and the plurality of substratescan subsequently be assembled together.

Whether a single substrate or a plurality of substrates is used, thepatterns in a multi-layer article generally need to be registered withrespect to each other. Herein, the terms “registration” and “alignment”refer synonymously to providing a desired geometrical relationshipbetween patterns formed on a substrate. Typically a multi-layer deviceor circuit has degraded performance if the patterned layers are notregistered to within a given set of tolerances.

Conventionally, alignment structures are formed as part of at least oneof the patterns of a multi-layer article and the locations of thealignment structures are determined optically. Positioning of asubsequent pattern formed on a substrate, or positioning of a secondpatterned substrate, is done with reference to the optically determinedlocation of the alignment structures.

Formation of the patterns can be done by additive processing or bysubtractive processing. In additive processing the pattern is formed asmaterial is deposited on the substrate. Printing of a pattern is anexample of additive processing. Printing can be done in analog fashion,as material is transferred from a master pattern or printing plate tothe substrate. Alternatively, printing can be done digitally as acontroller controls a printhead, for example, to deposit dots ofmaterial at specified locations in order to form the pattern. A familiarexample of multi-layer printing is the color printing of images, wheresuccessive layers of cyan, magenta, yellow (and optionally black orother color) inks are deposited in registration with each other. In manytypes of printing systems alignment marks are printed in a first layernear a plurality of edges (typically opposite edges) of the substrate.Cameras or other optical sensing devices are used to monitor thelocations of the alignment marks. The analog or digital printing of oneor more subsequently printed layers can be controlled using spatialadjustment of the printing device or the substrate so that thesubsequent printed layer is registered with reference to the alignmentmarks. For printing systems where the printhead or the substrate aremoved in a nominally linear fashion with respect to each other, thetiming of the printing of the subsequent layer(s) can also be controlledon the basis of identified locations of the alignment marks to helpprovide registration of the patterns. Location of the alignment marks atthe outside margins of the substrate can be advantageous both from thestandpoints of a) improved angular registration by locating thealignment marks far apart, and b) ability to subsequently remove themargins and the alignment marks in the finished multi-layer article.

Formation of patterns can also be done using subtractive processing. Insubtractive processing a blanket layer is typically formed on thesubstrate. Then material is selectively removed to form the pattern. Afamiliar example is the processing of semiconductor devices asschematically shown in FIGS. 1A and 1B using a mask aligner 10. A firstlayer of material can be deposited on the substrate 50. Photoresist 58can be deposited on the first layer. The photoresist is then exposedwith radiation 25 from an exposure station 20 of the mask aligner 10,typically through a first mask 30 having both the desired first pattern32 and alignment marks 35 and 36 to be associated with the first layer.In the example of FIG. 1A, the pattern 32 is a four by four array ofboxes 34 and the alignment marks 35 and 36 are cross-hairs. Thephotoresist 58 is developed so that the negatives of pattern 32 and thealignment marks 35 and 36 are no longer covered by photoresist. (Forsimplicity, the positive image rather than the negative image of four byfour pattern 52 of boxes 54 and alignment marks 55 and 56 in photoresistlayer 58 is shown in FIG. 1A.) The corresponding exposed areas of thefirst layer of material are subsequently etched away, resulting in thesubstrate 50 shown in FIG. 1B with the four by four pattern 62 of boxes64 and cross-hair alignment marks is formed on the surface of thesubstrate 50. The remaining photoresist 58 is also removed. A secondlayer (not shown) can then be deposited on the first patterned layer.Photoresist (not shown) can be deposited on the second layer. A secondmask 40 is then used to delineate a second pattern 42 in photoresist inregistration with the first patterned layer. In particular, cameras 15of the mask aligner are used to view substrate 50 through second mask 40as shown in FIG. 1B. The second pattern 42 in this example is a four byfour array of circles 44. The desired registration of the second pattern42 on second mask 40 to the first pattern in this example is when eachof the circles 44 is located at the center of a corresponding one of theboxes 64. Mask aligner 10 is used to move second mask 40 or substrate 50in the X, Y and θ directions until alignment marks 45 and 46 on secondmask 40 are registered with corresponding alignment marks 65 and 66formed in the first layer of material on wafer 50. In the example shownin FIG. 1B, alignment marks 45 and 46 are clear cross-hairs in an opaquefield. The clear cross-hairs 45 and 46 are typically designed to beslightly larger than the cross-hairs 65 and 66, so that it is easier todetect when cross-hairs 65 and 66 are centered within clear cross-hairs45 and 46.

Optical alignment of a sequence of patterned layers works very well whenthe reference alignment structures can be readily detected optically.For example, if the alignment features have a significantly differentreflectance or color than the substrate on which they are formed, thenthere is effective optical contrast between the alignment features andthe substrate.

In some types of multi-layer articles, patterns are formed usingmaterials that do not have effective optical contrast relative to theunderlying substrate. For example, it can be difficult to align withreference to an alignment mark that is formed of a substantiallytransparent material (that is, substantially transparent for thethickness of the patterned layer). Transparent materials can be used indisplays, in optical devices, in touch screen sensor films, inphotovoltaic devices, and in transparent electromagnetic shielding, forexample.

SUMMARY OF THE INVENTION

What is needed is a way to identify a location of an alignment markhaving poor optical contrast with respect to the substrate, and then touse the identified location as a basis for aligning one or moreadditional patterns with reference to a first pattern.

According to an aspect of the invention, a method for forming a secondpattern in registration with a first pattern on a substrate comprises,providing the substrate, the substrate having a first magnitude of anelectrical characteristic associated therewith, the substrate alsohaving a first pattern on a surface of the substrate, the first patternincluding at least one alignment structure that is associated with asecond magnitude of the electrical characteristic that is different fromthe first magnitude of the electrical characteristic of the substrate,using a controller to control an electrical probe to measure theelectrical characteristic corresponding to each of a plurality ofpositions proximate the substrate, wherein the measured electricalcharacteristic corresponds to the alignment structure when the probe isproximate to the alignment structure, and the measured electricalcharacteristic corresponds to the substrate when the probe is notproximate to the alignment structure, using a controller to interpretthe measured electrical characteristics for identifying a location ofthe alignment structure, and using a controller, responsive to theidentified location of the alignment structure, to control the formingof the second pattern so that it is in registration with the firstpattern.

The invention provides significant advantages over prior art methods andsystems. Location of an alignment mark having poor optical contrast withrespect to the substrate can be identified, and then used as a basis foraligning one or more additional patterns with reference to a firstpattern. The substrates and deposited patterns can be made oftransparent or substantially transparent materials enabling applicationssuch as touch-screens.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the invention are better understood with reference to thefollowing drawings. The elements of the drawings are not necessarily toscale relative to each other.

FIG. 1A shows a schematic of a prior art method of exposing aphotoresist pattern on a substrate through a first mask for subtractiveprocessing;

FIG. 1B shows a schematic of a prior art method of a aligning a secondmask relative to alignment marks formed on the substrate using the firstmask of FIG. 1B;

FIG. 2 shows a portion of system 100 for locating a pattern relative toan alignment structure by using measurements of an electricalcharacteristic according to an aspect of the invention;

FIGS. 3A and 3B shows sequences of moves of a probe for finding thelocation of an edge of an alignment structure;

FIG. 4A shows a configuration of a resistance probe unit;

FIG. 4B shows a schematic for measuring resistance via currentmeasurement using the probe unit of FIG. 4A;

FIGS. 4C through 4F show a sequence of moves of the probe unit of FIG.4A for identifying the location of an alignment structure;

FIG. 5 shows a partially exploded view of a portion of the system ofFIG. 2 for aligning a second substrate to a first substrate;

FIG. 6 shows a portion of the system of FIG. 2 for forming a secondpattern in alignment with a first alignment structure;

FIG. 7 shows a plurality of patterns on a substrate and a portion of thesystem of FIG. 2;

FIGS. 8A and 8B show configurations of capacitance probes;

FIG. 9 is a schematic side view of a flexographic printing system thatcan be used in roll-to-roll aspects of the invention;

FIG. 10 shows a portion of a printing system that can be used in aspectsof the invention;

FIGS. 11A and 11B show configurations of a resistance probe unit;

FIG. 12 shows a perspective of an alignment structure configurationaccording to an aspect of the invention;

FIG. 13A shows a top view of an alignment structure similar to thatshown in FIG. 12;

FIG. 13B shows a top view of an alternate alignment structureconfiguration;

FIG. 14A shows a top view of an alignment structure configurationaccording to an aspect of the invention;

FIG. 14B shows a schematic for measuring resistance via currentmeasurement; and

FIG. 14C shows current readings for the alignment structureconfiguration of FIG. 14A corresponding to preferred alignment in thecross-track direction with no skew;

FIG. 14D shows current readings corresponding to misalignment in thecross-track direction;

FIG. 14E shows current readings corresponding to skew error;

FIGS. 15A and 15B show further alignment structure configurationsaccording to aspects of the invention;

FIG. 16 shows a flowchart for a method for aligning patterns on twosubstrates according to an aspect of the invention; and

FIG. 17 shows a flowchart for a method for aligning two patterns on asubstrate according to an aspect of the invention.

DETAILED DESCRIPTION

Throughout the specification and claims, the following terms take themeanings explicitly associated herein, unless the context clearlydictates otherwise. The meaning of “a,” “an,” and “the” includes pluralreference, the meaning of “in” includes “in” and “on.” Additionally,directional terms such as “on”, “over”, “top”, “bottom”, “left”, “right”are used with reference to the orientation of the Figure(s) beingdescribed. Because components of aspects of the present invention can bepositioned in a number of different orientations, the directionalterminology is used for purposes of illustration only and is in no waylimiting.

The present description will be directed in particular to elementsforming part of, or cooperating more directly with, a system inaccordance with the present invention. It is to be understood thatelements not specifically shown, labeled, or described can take variousforms well known to those skilled in the art. In the followingdescription and drawings, identical reference numerals have been used,where possible, to designate identical elements. It is to be understoodthat elements and components can be referred to in singular or pluralform, as appropriate, without limiting the scope of the invention.

The example aspects of the present invention are illustratedschematically and not to scale for the sake of clarity. One of ordinaryskill in the art will be able to readily determine the specific size andinterconnections of the elements of the example aspects of the presentinvention.

Aspects of the invention rely on the use of electrical measurements toidentify the location of alignment features formed in association with afirst pattern for use in aligning one or more additional patterns withreference to the first pattern. This requires that there be effective“electrical contrast” between the alignment structure and the substrateon which it is formed. Electrical properties of materials includeresistivity (or conductivity) as well as dielectric constant forexample.

Although in general the invention is useful for any combination ofsubstrate material and pattern layer material having poor opticalcontrast but effective differentiation using appropriate electricalmeasurements, a particular class of patterned materials of interest isthe class of transparent conductive films. Transparent conductive filmscan be used in displays, in optical devices, in touch screen sensorfilms, in photovoltaic devices, and in transparent electromagneticshielding, for example.

Table 1 lists electrical resistivity ρ for a variety of substratematerials. Thermal silicon oxide is a thermally grown oxide layer thatis typically formed on silicon to provide electrical insulation. Hereinwhen we refer to forming a pattern on substrate, the substrate caninclude not only the underlying bulk substrate, but also one or morelayers that have previously been formed on the bulk substrate andlocated below the patterned layer. Table 2 lists electrical resistivityρ for a variety of transparent conductive films.

TABLE 1 Electrical resistivity ρ for some substrate materials SubstrateMaterial Resistivity (ohm - meter) Silicon 6.4 × 10² Thermal siliconoxide 10¹⁴ Glass 10¹⁰ to 10¹⁴ Polyethylene terephthalate (PET) 10²¹

TABLE 2 Electrical resistivity ρ for some transparent conductive filmsTransparent Conductive Material Resistivity (ohm - meter) Graphene 10⁻⁸PEDOT - PSS 10⁻³ to 10⁻¹ Indium tin oxide 10⁻⁶

One class of transparent conductive materials is doped metal oxides,such as indium tin oxide (tin-doped indium oxide), aluminum-doped zincoxide, and indium-doped cadmium oxide. Another class of transparentconductive materials is transparent conducting organic materialsincluding graphene, carbon nanotubes and polymers such as the PEDOTfamily of materials. PEDOT is the commonly used name forpoly(3,4-ethylenedioxythiophene). Doping PEDOT with polystyrenesulfonate) can improve the properties over the unmodified PEDOT. ThisPEDOT-PSS compound has become an industry leader in transparentconductive polymers. Where transparency is a desired factor, transparentconductive films can have a light transmittance between 80% and 100%.Transparent conductive polymers can be further advantaged in combinationwith flexible substrates such as PET, since the transparent conductivepolymers can also be flexible.

FIG. 2 shows a portion of system 100 for locating an alignment structureby measurements of an electrical characteristic for alignment of apattern. System 100 includes a support 110 disposed along an X-Y planefor a first substrate 150 on which one or more first alignmentstructures 152 are formed, as well as a first pattern 154. In thisexample, first alignment structures 152 and first pattern 154 are shownin dashed lines to indicate that they are substantially transparent.Herein substantially transparent is defined as having a lighttransmittance of 75% or more. Optionally, support 110 includes amechanical registration feature 112 for coarse alignment of firstsubstrate 150. Also optionally, support 110 includes a hold-downmechanism, such as a vacuum hold-down for holding first substrate 150 ina stationary position. Vacuum holes 114 are shown in FIG. 2 as locatedbeyond the left edge of first substrate 150. Similar vacuum holes (notshown) can be arrayed across the area of support 110 that is covered byfirst substrate 150. Alternative types of hold-down mechanisms includeelectrostatic hold-down and mechanical clamps.

System 100 is configured to measure electrical resistance using firstprobe 131 and second 133. In the aspect of the invention shown in FIG.2, the first probe 131 is a fixed resistance probe and the second probe133 is a movable resistance probe. Movable probe 133 is moved to aplurality of positions proximate first substrate 150 for taking themeasurements. In the example shown in FIG. 2, system 100 includes afirst mover 141 for moving movable probe 133 along the X directionparallel to the support 110, a second mover 142 for moving movable probe133 along the Y direction parallel to the support 110, and a third mover143 for moving movable probe 133 along the Z direction perpendicular tothe support 110. Controller 120 controls the first, second and thirdmovers 141, 142 and 143 using mover control module 126. In some aspectsof the invention, first pattern 154 and first alignment structures 152have been formed on first substrate 150 with reference to the same or asimilar feature as mechanical registration feature 112, so that theapproximate position of at least one first alignment structure 152 isknown. The first alignment structure 152 has a large enough region thatthe probe tip 132 of fixed probe 131 can be placed with reasonableconfidence on alignment structure 152.

Movable probe 133 is moved to a plurality of positions for takingresistance measurements. Because of the large differences in resistivitybetween typical substrate materials (Table 1) and typical transparentconductive materials (Table 2) it is easy to distinguish when probe tip134 of movable probe 133 is in contact with or out of contact with thefirst alignment structure 152 in contact with fixed probe 131. Theresistance measured by the two probes is equal to ρl/wt, where l is thelength of the current path (that is, the distance between probe tips 132and 134), w is the “effective width” of the current path, and t is thethickness of the current path. The effective width of the current pathwould be the actual width of the alignment structure if the probes wereparallel line contacts across a finite width conductive stripe, or ifthe point contacts were very far apart on a narrow conductor. Using theformula ρl/wt and the actual width will result in some amount of errorin a resistance measurement using two probe points. However, for manycases of interest it is not the exact value of the resistancemeasurement that is of interest, but rather the large change inresistance value when both probes contact the conductive alignmentstructure relative to one or both probes not contacting the alignmentstructure. In addition, as described below, in some aspects of theinvention, resistance itself is not separately determined. Rather, acurrent that depends on resistance is measured due to an appliedvoltage, or a voltage that depends on resistance is measured due tocurrent applied through a current source.

For a layer of substantially constant thickness t (such as the layerforming the first alignment structure), one can refer to the sheetresistance equal to ρ/t as the electrical characteristic. The thicknessof first substrate 150 is typically much thicker (on the order of 0.1 mmto 2 mm) than the thickness (0.001 mm or less) of first alignmentstructure 152, but the differences in resistivities are sufficient tomake it clear when probe tip 134 is in contact with or out of contactwith first alignment structure 152. What is actually measured betweenthe two resistance probes is resistance (voltage divided by current).Typically the resistance measured when both probe tips 132 and 134 arecontacting first alignment structure 152 is less than 1% of theresistance measured when probe tip 134 is not contacting first alignmentstructure 152. The location of the first alignment structure 152 can beidentified by a change of measured value between measurement locationsthat exceeds a predetermined threshold. The predetermined threshold canbe set to provide effective differentiation by the controllers betweenthe measured electrical characteristic at locations corresponding to thesubstrate and the alignment structure. In the above example, a thresholdcorresponding to a change in the resistance of 100 times or more can beused. Although in many cases of interest the alignment structure is moreconductive than the underlying substrate, the location of anelectrically insulating or resistive alignment structure covering aconductive substrate or surrounded laterally by an electricallyconductive layer can also be identified.

An edge of alignment structure 152 can be identified as lying betweenthe position of a measurement of high resistance (probe tip 134 on thesurface of first substrate 150) and a measurement of comparatively lowresistance (probe tip 134 contacting first alignment structure 152. Thecloser the two measurement positions are, the more accurately thelocation of the edge of the alignment structure can be determined. Inthe example shown in FIG. 2, by moving movable probe 133 along the Xdirection using first mover 141 and measuring resistance valuescorresponding to each of a plurality of positions along the X direction,one or more edges of the leg of first alignment structure 152 thatextends along the Y direction can be located. Because there can be somemanufacturing variation in the width of first alignment structure 152,it can be useful to identify and locate two opposite edges of the legextending along the Y direction (a first edge on a first side of the legand a second edge on a second side of the leg) and define the locationof the leg of the first alignment structure 152 with respect to a centerposition midway between the opposite edges of the leg. Similarly, bymoving movable probe 133 along the Y direction using second mover 142and measuring resistance values corresponding to each of a plurality ofpositions along the Y direction, one or more edges of the leg of firstalignment structure 152 that extends along the X direction can belocated. Again, because of manufacturing variation in the width ofalignment structure 152, it can be useful to identify and locate twoopposite edges of the leg extending along the X direction.

In the aspect of the invention shown in FIG. 2, movable probe 133 israised up during its moves between measurement positions, so that thereis a gap g between the probe tip 134 and the surface of first substrate150. In other aspects of the invention, movable probe tip 134 is held incontact with first substrate 150 during movement between measurementpositions.

In addition to mover control module 126 described above, controller 120also includes measurement module 122 for performing the resistancemeasurements, and interpreting the resistance measurements for locatingfirst alignment structures 152. Mover control module 126 controls thedistance moved by first mover 141 and second mover 142 so thatmeasurement module can analyze resistance as a function of position ofmovable probe 133. Registration module 124 controls the recording of thelocation of the first alignment structure for use in aligning one ormore additional patterns to first pattern 154. In some aspects of theinvention, registration module 124 can include a memory. In otheraspects of the invention, registration module 124 controls a markingstation 160 for providing at least one reference mark 164 on the firstsubstrate 150 at a predetermined distance and direction from theidentified location of first alignment structure 152. Reference mark 164can be observed optically or it can be used as a mechanical registrationmark. Marking station 160 includes a marking element 162 that caninclude at least one of an ink marker, a laser, a blade, a hole punch,an indenter, a drill or a heated tip.

In some aspects of the invention, rather than moving the probe 133 whilekeeping the first substrate 150 stationary, the probe 133 is held in afixed position and the first substrate 150 is moved. FIG. 2 shows anoptional first mover 191 for moving the substrate 150 (by moving support110) in the X direction, and an optional second mover 192 for moving thesubstrate 150 (by moving support 110) in the Y direction.

FIG. 3A shows a sequence of moves of movable probe 133 as controlled bycontroller 120 (FIG. 2) in order to find the location of edge 156 offirst alignment structure 152 on first substrate 150, where the distancemoved is a function of whether a high value or low value of resistanceis measured. In FIG. 3A it is assumed that fixed probe 131 is at contactposition 170. Movable probe 133 (FIG. 2) is controlled by controller 120to take a first measurement of resistance at first position 171. Since,in this example, first position 171 is not in contact with firstalignment structure 152, the first measured resistance is a high value.Then movable probe 133 is moved along the X direction by a firstdistance d1 to second position 172 and a second measurement ofresistance is taken at second position 172. Since, in this example,second position 172 is in contact with first alignment structure 152,the second measurement of resistance is a low value. Controller 120 isprogrammed to know the width of the leg of first alignment structure 152in the X direction, so as it controls movable probe 133 to move a seconddistance d2 to a third position 173, the distance d2 moved along Xcontrolled to be less than the known width of the leg. In addition, d2is typically less than d1 if controller 120 recognizes that movableprobe 133 is in already in contact with first alignment structure 152 atsecond position 172. Movement by a third distance (not shown) along theX direction to a fourth position would typically be less than or equalto second distance d2 if the controller recognizes that movable probe isstill in contact with first alignment structure 152 at third position173. Successive moves and measurements can be made until a high value ofresistance is again measured, corresponding to a position (not shown)that is beyond edge 156 of first alignment structure 152.

FIG. 3B shows a sequence of moves of movable probe 133 as controlled bycontroller 120 (FIG. 2) in order to find the location of edge 156 offirst alignment structure 152 on first substrate 150, where a high valueof resistance is recorded at both the first and second positions. InFIG. 3B it is assumed that fixed probe 131 at contact position 170.Movable probe 133 (FIG. 2) is controlled by controller 120 to take afirst measurement of resistance at first position 176. Since, in thisexample, first position 176 is not in contact with first alignmentstructure 152, the first measured resistance in this example is a highvalue. Then movable probe 133 is moved along the X direction by a firstdistance s1 (where s1 is larger than the known width of the leg of thefirst alignment structure 152) to second position 177 and a secondmeasurement of resistance is taken at second position 177. Since, inthis example, second position 177 is also not in contact with firstalignment structure 152, the second measurement of resistance in thisexample is also a high value. In the sequence of moves shown in FIG. 3B,the controller 120 (FIG. 2) controls the movable probe to move it by asecond distance s2 less than first distance s1 in a direction oppositethe X direction. In this example, moving from first position 176 to 177skips past edge 156 of first alignment structure 152. Moving a smallerdistance s2 in the opposite direction results in movable probe 133contacting first alignment structure 152 at third position 178 so that alow value of resistance is recorded. A succession of moves along thesame direction (as in FIG. 3A) or in opposite directions (as in FIG. 3B)can be used iteratively to locate edge 156 with sufficient accuracy.

In some aspects of the invention, the electrical probes can beintegrated together in a probe unit. FIG. 4A shows an example of a probeunit 220 having a first contact element 221, a second contact element222 and a third contact element 223 that are electrically insulated fromeach other and arrayed in a nonlinear fashion. Each of the contactelements includes a contact surface 225. First contact element 221 canbe a reference probe, where second contact element 222 is displaced fromfirst contact element 221 by a distance D_(x) along the X direction, andthird contact element 223 is displaced from first contact element 221 bya distance D_(y) along the Y direction. FIG. 4B shows an example of acircuit for measuring resistance. What is actually measured is a currentwhose value depends on the resistance between two contact elements. Afirst voltage V₁ and a first current measuring device I₁ are connectedbetween first contact element 221 and second contact element 222. Asecond voltage V₂ and a second current measuring device I₂ are connectedbetween first contact element 221 and third contact element 223. If bothfirst contact element 221 and second contact element 222 are in contactwith the same conductive surface, such as a conductive alignmentstructure, then first current measuring device I₁ will measure asignificantly higher current than if either first contact element 221 orsecond contact element 222 is not in contact with the same conductivesurface. Similarly, if both first contact element 221 and third contactelement 223 are in contact with the same conductive surface, such as aconductive alignment structure, then first current measuring device I₂will measure a significantly higher current than if either first contactelement 221 or third contact element 223 is not in contact with the sameconductive surface.

FIGS. 4C through 4F show a sequence of relative movements of probe unit220 and an alignment structure 226. With reference to FIG. 2, alignmentstructure 226 is formed on a substrate 150, preferably in at leastcoarse alignment with edges that can be mechanically registered bymechanical registration feature 112. In this way a starting point forfinding the location of edges of alignment structure 226 can beprovided. It is assumed that alignment structure 226 has a muchdifferent resistance as measured between two points than does theunderlying substrate (not shown in FIGS. 4C through 4F). For examplesubstrate 150 can be a substantially insulating substrate and alignmentstructure 226 can be formed of a conductive material. Alignmentstructure 226 in this example is a rectangle having sides a along the Xdirection and b along the Y direction. Side a is made to be larger thanthe contact element spacing D_(x) of probe unit 220, and side b is madeto be larger than the contact element spacing D_(y).

In FIG. 4C probe unit 220 is positioned by a controller to be nearalignment structure 226 and offset along the Y direction so that it isnot in contact. Probe unit 220 is then moved along the Y directiontoward alignment structure 226. In FIG. 4D both first contact element221 and second contact element 222 are in contact with alignmentstructure 226 (assumed here to be conductive), so that I₁ (FIG. 4B)indicates a high current. However, third contact element 223 is not incontact with alignment structure 226, so that I₂ indicates a lowcurrent. In FIG. 4E third contact element 223 has just contacted firstedge 227 (FIG. 4C) of alignment structure 226, as is detected by a lowto high current transition at I₂ that is greater than a predeterminedamount. At this point, the relative motion of probe unit 220 in the Ydirection is stopped, and motion in the −X direction begins. Adjacentedge 228 is identified when a high to low current transition is sensedin I_(l) that is greater than a predetermined amount. In this way bothfirst edge 227 and adjacent edge 228 are identified, thereby identifyingthe location of alignment structure 226.

FIG. 5 shows a partially exploded view of another portion of system 100of FIG. 2. The portion of system 100 shown in FIG. 5 is configured toalign a second substrate 250 having a second pattern 254 formed thereonrelative to the first alignment structure(s) 152 on first substrate 150.In this example, second pattern 254 includes a two by two array ofcircles that are intended to be centered with respect to the two by twoarray of boxes of first pattern 154 on first substrate 150. Secondpattern 254 can also be substantially transparent and have substantiallytransparent second alignment structures 252 associated with it. It isassumed in the example of FIG. 5 that the location of second alignmentstructures 252 have already been determined, for example, as describedabove relative to first alignment structures 152, and that at least onecorresponding reference mark 264 has been formed on second substrate 250at the predetermined distance and direction from the identified locationof second alignment structure(s) 252. Second alignment structures 252 inFIG. 5 include rectangles that are intended to nest within the insidecorners of the L-shaped first alignment structures 152.

When the second alignment structures 252 are in registration with thefirst alignment structures 152, then the two by two array of circles ofsecond pattern 254 is in registration with the two by two array of boxesof first pattern 154. However, if both the first alignment structures152 and the second alignment structures 252 are substantiallytransparent, it can be difficult to directly use conventional opticalalignment methods. Two alternative different indirect alignment methodsare shown for aligning second pattern 254 on second substrate 250 tofirst pattern 154 on first substrate 150 using first alignment structure152 and second alignment structure 252. In particular, reference mark(s)164 formed at a predetermined distance and direction from the identifiedlocation of first alignment structure(s) 152 are aligned withcorresponding reference mark(s) formed at the predetermined distance anddirection from the identified location of second alignment structure(s)252. If reference marks 164 and 264 are mechanical registration marks(such as holes punched in first substrate 150 and second substrate 250by marking element 162 (FIG. 2), then a mechanical registration member,such as pin(s) 190 can be used to register the second pattern 254 to thefirst pattern 154 by inserting pin(s) 190 into each set of correspondingreference marks 164 and 264. Alternatively, if reference marks 164 and264 are optically detectable (such as registration marks made by amarking element 162 that includes an ink marker), then an opticalregistration member, such as camera(s) 195) can be used to register thesecond pattern 254 to the first pattern 154 by optical alignment of eachset of corresponding visible reference marks 164 and 264.

In order to move second substrate 250 such that second pattern 254 isaligned with respect to first alignment structures 152 on firstsubstrate 150, a registration mechanism can include a positioner 180.Second substrate 250 can be held in place on positioner 180 usingvacuum, electrostatic force, or mechanical clamps for example.Controller 120 can be used to move second substrate 250 along the X andY directions to align the second substrate 250 and then move it alongthe Z direction to bring the second substrate 250 into contact with thefirst substrate 150 for assembly, optionally with the aid of an adhesive(not shown).

In some aspects of the invention, the second alignment structure 252 isnot transparent, so that its location can be optically identified priorto aligning the second substrate 250 relative to the first substrate150. In such a case it can be advantageous to form first reference mark164 coincident with the location of the first alignment structure 152(that is, forming the first reference mark 164 at zero distance from theidentified location of the first alignment structure. Then the secondalignment structure(s) 252 can be optically aligned to first referencemark(s) 164 using camera(s) 195.

In some aspects of the invention, alignment of a second pattern to afirst pattern includes forming the second pattern on the first substrate150 in alignment with the first alignment structure 152, rather thanaligning a second substrate 250 to the first substrate 150 as describedabove. FIG. 6 shows a portion of system 100 (see also FIG. 2) configuredfor forming the second pattern in registration with the first alignmentstructures 152 whose locations were previously identified usingelectrical measurements. In FIG. 6 a pattern forming station 200 ispositioned proximate the same side 151 of first substrate 150 on whichfirst pattern 154, first alignment structures 152, and optionallyreference mark(s) 164 are formed. Controller 120 can be used to controlpattern forming station 200 to form a second pattern (such as secondpattern 254 shown in FIG. 5) on the same side 151 of first substrate 150as first pattern 154. Pattern forming station 200 can include an analogprinting member, such as a flexographic printing plate, or a digitalprinthead, such as an inkjet printhead for example. Controller 120 canuse locations of first alignment structures 152 previously identifiedand stored in memory, or it can control pattern forming station 200relative to reference mark(s) 164 made previously relative to firstalignment structures 152. The registration mechanism in these aspects ofthe invention includes the controller 120 and the pattern formingstation 200 for forming the second pattern 254 in registration with theidentified location of the first alignment structures.

Also shown in FIG. 6 is a second pattern forming station 210 positionedproximate the opposite side 153 of first substrate 150 as the side 151on which first pattern 154, first alignment structures 152, andoptionally reference mark(s) 164 are formed. Controller 120 can be usedto control pattern forming station 210 to form a second pattern (such assecond pattern 254 shown in FIG. 5) on the opposite side 153 of firstsubstrate 150 as first pattern 154. Although support 110 holds firstsubstrate 150, it is assumed here that portions of support 110 areremoved that would otherwise interfere with pattern forming station 210forming second pattern 254 on the opposite side 153.

In some aspects of the invention, alignment structures such as secondalignment structures 252 shown in FIG. 5 are also formed on substrate150. For instances where second alignment structures 252 are alsosubstantially transparent but have values of an electricalcharacteristic different from that of first substrate 150, the locationsof second alignment structures 252 can also subsequently be identified(for aligning additional subsequent patterns for example) usingelectrical measurements as described earlier.

In some aspects of the invention, as illustrated in FIG. 7, a pluralityof first substantially transparent patterns 154 are formed on firstsubstrate 150, where each of the plurality of first substantiallytransparent patterns 154 includes at least one first alignment structure152 having a magnitude of the electrical characteristic that isdifferent from a magnitude of the electrical characteristic of the firstsubstrate 150. First probe 131 and second probe 133 can be used tomeasure values of the resistance as a function of position as describedabove in order to identify the locations of the first alignmentstructures 152, and optionally marking station 160 can form referencemarks 164. Subsequently, first substrate 150 can be divided alongseparation lines 158 into a plurality of substrate pieces 159, such thateach of the plurality of substrate pieces 159 includes one of theplurality of first substantially transparent patterns 154.

Electrical probes described above have been resistance probes thatrequire contact with the alignment structure during measurement.Alternatively a capacitance probe 135 can be used to measure values ofcapacitance as a function of position (while out of contact with firstsubstrate 150) as the capacitance probe 135 and the first substrate 150are moved relative to each other in the X or Y directions as shown inFIGS. 8A and 8B. In the configuration shown in FIG. 8A, a pair of plates136 and 137 are laterally displaced and electrically insulated from eachother on capacitance probe 135. An AC voltage V is applied betweenplates 136 and 137, and a resulting electrical signal (not shown) ismonitored. First alignment structure 152 can have a differentresistivity or dielectric constant relative to first substrate 150. InFIG. 8B the plates 136 and 137 of capacitance probe 135 are parallel toeach other and located on opposite sides of first substrate 150. As thecapacitance probe is moved relative to the first substrate 150, changesin the resulting signal are used to determine the location of thealignment structure 152.

FIG. 9 is a schematic side view of a flexographic printing system 300that can be used in aspects of the invention for roll-to-roll printingon one or both sides of a flexible substrate 350, where alignment ofsuccessive printed patterns is performed using electrical measurementsto identify locations of alignment structures. Substrate 350 is fed as aweb from supply roll 302 to take-up roll 304 through flexographicprinting system 300. Advancement of the web can be done by a main driveroller (not shown) at or near take-up roll 304. Other drives (not shown)can be used to adjust the local speed and tension in the web. Substrate350 has a first side 351 and a second side 352 opposite first side 351.Optionally substrate 350 is a transparent film such as PET.

The flexographic printing system 300 includes two print modules 310 and330 that are configured to print on the first side 351 of substrate 350,as well as two print modules 320 and 340 that are configured to print onthe second side 352 of substrate 350. The web of substrate 350 travelsoverall in roll-to-roll direction 305 (left to right in the example ofFIG. 9). However, various rollers 306 and 307 are used to locally changethe direction of the web of substrate as needed for adjusting webtension, providing a buffer, and reversing a side for printing. Inparticular, note that in print module 320 roller 307 serves to reversethe local direction of the web of substrate 350 so that it is movingsubstantially in a right-to-left direction.

Each of the print modules 310, 320, 330, 340 include some similarcomponents including a respective plate cylinder 311, 321, 331, 341, onwhich is mounted a respective flexographic printing plate 312, 322, 332,342, respectively. Each flexographic printing plate 312, 322, 332, 342has raised features 313 defining an image pattern to be printed on thesubstrate 350. Each print module 310, 320, 330, 340 also includes arespective impression cylinder 314, 324, 334, 344 that is configured toforce a side of the substrate 350 into contact with the correspondingflexographic printing plate 312, 322, 332, 342.

Each print module 310, 320, 330, 340 also includes a respective aniloxroller 315, 325, 335, 345 for providing ink to the correspondingflexographic printing plate 312, 322, 332, 342. As is well known in theprinting industry, an anilox roller is a hard cylinder, typicallyconstructed of a steel or aluminum core, having an outer surfacecontaining millions of very fine dimples, known as cells. The aniloxrollers 315, 325, 335 and 345 receive the ink from ink pans or inkreservoir chambers (not shown). In some aspects of the invention, someor all of the print modules 310, 320, 330, 340 also include respectiveUV curing stations 316, 326, 336, 346 for curing the printed ink onsubstrate 350.

For conventional roll-to-roll printing of registered patterns on asubstrate 350 by successive print modules 310, 320, 330 and 340, opticalalignment of alignment structures would generally be used. However, whenprinting transparent patterns onto substrate 350, optical alignment canbe difficult. According to aspects of the invention, electricalmeasurements using a probe (in similar fashion as described above) canbe used to identify the locations of alignment structures, as long asthere is sufficient “electrical contrast” between the measuredelectrical characteristic for the alignment structure and the substrate350.

In a roll-to-roll printing system, such as flexographic printing system300, the substrate 350 is moved along a path called the in-trackdirection from supply roll 302 to take-up roll 304. Although the pathtypically winds around various rollers as shown in FIG. 9, the pathincludes substantially straight segments in which substrate 350 moves ina predetermined substantially linear direction. Since the substrate 350is moved in a roll-to-roll printing system, the electrical probe can beheld in a fixed position, while the substrate 350 and alignmentstructures move past the stationary probe. FIG. 9 shows three stationaryelectrical probes 317, 327 and 337, as well as the correspondingcontrollers 318, 328 and 338. Probe 317 and controller 318 are used toidentify locations of alignment structures formed on first side 351 ofsubstrate 350 by print module 310. Probe 327 and controller 328 are usedto identify locations of alignment structures formed on second side 352of substrate 350 by print module 320. Probe 337 and controller 338 areused to identify locations of alignment structures formed on first side351 of substrate 350 by print module 330. Identified locations ofalignment structures can be stored in memory that can be included incontrollers 318, 328 and 338, for example. Each of the probes 317, 327and 337 is shown as positioned opposite a corresponding roller 319, 329,and 339 in order to stabilize the motion of the web of substrate 350 inthe regions where electrical measurements are made.

The various print modules 310, 320, 330 and 340 include correspondingprinting plates 312, 322, 332 and 342 that serve as pattern formingstations and are generally located between the supply roll 302 and thecorresponding stationary probe 317, 327 and 337. Printing plate 322 ofsecond print module 320 is located between stationary probe 317 andtake-up roll 304. In the example of FIG. 9, there is no stationary probedownstream of the final printing plate 342, since no subsequent patternsneed to be aligned to patterns printed by print module 340. However,there is a controller 348 for adjusting registration of patterns printedby fourth printing module 340. UV curing stations 316, 326 and 336 arelocated between corresponding printing plate 312, 322, and 332 andcorresponding probes 317, 327 and 337.

As disclosed above, a gap can be provided between the surface ofsubstrate 350 and the stationary probes 317, 327 and 337. Alternatively,the stationary probes 317, 327 and 337 can be configured to contact thesurface of substrate 350. In order to keep a contact probe from removingportions of the alignment structures by scratching, the probe tip canhave a rounded surface. (See FIGS. 11A and 11B.) Optionally the probetip can have a rotatable surface, such as a rotatable ball (similar to aballpoint pen), a rotatable cylinder or a wheel.

The stationary probes 317, 327 and 337 can be capacitance probes if themeasured electrical characteristic is capacitance, or resistance probesif the measured electrical characteristic is resistance. Capacitanceprobes can have elements disposed on opposite sides of the substrate asshown in FIG. 8B. In some aspects of the invention, one element of thecapacitance probe can be metal roller 319, 329 or 339.

After location of an alignment structure printed by first print module310 has been determined by probe 317 and controller 318, the informationis used to adjust the operation of the flexographic printing system 100in order to form patterns by at least one successive print module 320(on second side 352), or print module 330 (on first side 351) or printmodule 340 (on second side 352) in registration with the pattern andalignment structure printed by first print module 310 on first side 351of substrate 350. In order to adjust the printing position of asubsequent pattern printed by a subsequent print module along thein-track direction (that is, to correct the longitudinal position), oralong the cross-track position (that is, into or out of the plane ofFIG. 9 to correct for lateral registration), or to correct for skewerror, measures such as those described in U.S. Pat. No. 4,534,288 canbe taken.

A portion of printing system 400 is shown in FIG. 10. Web of substrate450 is advanced along advancement direction 405 by drive roller 410.First pattern forming station 401 (for example a printhead) forms firstpattern 454 and a plurality of first alignment structures 452 and 455 ina series of frames 459. Frames 459 are bounded at each end by separationlines 458. Separation lines 458 can be printed on substrate 450, or theycan just represent the sites at which web of substrate 450 willsubsequently be cut into pieces. In the example shown in FIG. 10, thereare three frames between first pattern forming station 401 and secondpattern forming station 402, which is configured to print second pattern474 and a plurality of second alignment structures 472 and 475 inregistration with first alignment structures 452 and 455 respectively.First alignment structure 452 and second alignment structure 472 areprinted near first edge 456 of substrate 450. First alignment structure455 and second alignment structure 475 are printed near second edge 457of substrate 450. A first stationary probe 461 is located near firstedge 456 of substrate 450 in order to make electrical measurements inline with first alignment structures 452 as substrate 450 moves pastalong advancement direction 405. A second stationary probe 462 islocated near second edge 457 of substrate 450 in order to makeelectrical measurements in line with first alignment structures 455 assubstrate 450 moves past along advancement direction 405. Roller 411supports web of substrate 450 near first stationary probe 461, androller 412 supports web of substrate 450 near second stationary probe462. An encoder (not shown) can be attached to roller 411 or roller 412,for example, in order to monitor the movement of substrate 450. Firstcontroller 463 receives measurement signals from first stationary probe461 and interprets them to identify positions of first alignmentstructures 452. Second controller 464 receives measurement signals fromsecond stationary probe 462 and interprets them to identify positions offirst alignment structures 455. First and second controllers 463 and 464can include memories for storage of alignment structure locations.Second pattern forming structure 402 is controlled to print secondpattern 474 in registration with first pattern 454 based on informationprovided first and second controllers 463 and 464. In the example shownin FIG. 10, first pattern 454 is a two by two array of boxes and secondpattern 474 is a two by two array of circles. When second pattern 474 isregistered to first pattern 454, the circles are positioned in thecenters of the boxes, and the second alignment structures 472 and 475are aligned with respect to first alignment structures 452 and 455respectively.

As indicated above with reference to FIG. 4A, a plurality of probeelements can be incorporated together in a single probe unit. In FIG.11A, probe unit 510 includes two contact elements 511 and 512 that areelectrically insulated from each other and spaced apart by a distanceD₁. For aspects of the invention where the tips of contact elements 511and 512 are held in contact with the substrate as the probe unit 510 andthe substrate are moved relative to each other, it can be advantageousfor contact elements 511 and 512 to have a rounded contact surface 515.Optionally, rounded contact surface can be rotatable. In FIG. 11B, probeunit 520 includes a first contact elements 521, a second contact element522 and a third contact element 523 that are electrically insulated fromeach other and are arrayed in linear fashion, such that second contactelement 522 is between first contact element 521 and third contactelement 523. First and second contact elements 521 and 522 are spacedapart by a distance D₁, and second and third contact elements 522 and523 are spaced apart by a distance D₂. In some aspects of the invention,as discussed below, it can be advantageous if D₂ is greater than D₁.

In a system where the relative motion of the substrate and the probe isin a single linear direction, such as advancement direction 405(nominally the X direction) in FIG. 10, it is useful to be able todetermine alignment information along both the X direction and the Ydirection using relative motion only in the X direction. FIG. 12 shows aperspective of an alignment structure configuration that can providealignment information along both the X direction and the Y directionusing a resistance measurement as the substrate is moved relative to theprobe in the X direction. First and second alignment structures 610 and616 can be formed during the same pattern forming operation that formspattern 654, so that determining the alignment location of first orsecond alignment structures 610 and 616 also provides information aboutthe location and orientation of pattern 654. First and second alignmentstructures 610 and 616 in FIG. 12 are not to scale, but are shown asrelatively large compared to pattern 654 in order to provide bettervisibility for the features of the alignment structures.

Pattern 654 as well as first and second alignment structures 610 and 616are indicated by dashed outlines to indicate that they are substantiallytransparent in this example. By substantially transparent it is meantthat they have a light transmittance greater than 75%, and morepreferably between 80% and 100%. In addition, substrate 650 has a highresistivity, for example as shown in Table 1 above, and first and secondalignment structures 610 and 616 have comparatively low resistivity, forexample as shown in Table 2 above. First and second alignment structures610 and 616 can be formed using materials such as an inorganic oxidefilm (for example indium tin oxide) or an organic film (for examplePEDOT, PDOT-PSS, graphene, or carbon nanotubes). Typically, alignmentstructures formed using a transparent conductive material have aresistivity between 10⁻⁸ ohm-meter and 1 ohm-meter. Properties statedbelow relative to first alignment structure 610 are also generallyapplicable to second alignment structure 616. Second alignment structure616 can be a mirror image of first alignment structure 610 for example.The resistance measured by two probe contact elements at a predetermineddistance between any two points on first alignment structure 610 is lessthan one percent of an electrical resistance of the substrate asmeasured by the same two probe contact elements at the samepredetermined distance. In other words, there is a large difference inthe value of resistance measured if both contact elements are in contactwith first alignment structure 610, relative to the much higherresistance measured if one or both contact elements are not in contactwith first alignment structure 610.

With reference to FIG. 12 and the top view of FIG. 13A, one (or more)first alignment structure(s) 610 is formed near first edge 656 ofsubstrate 650 and is designed to facilitate alignment by electricalresistance measurement. First alignment structure 610 includes areference member 615 that extends along the X direction, which isnominally the advancement direction 605; a first member 611 that isconnected to the reference member 615 and extends along a firstdirection (defined in this example to be the Y direction); and a secondmember 612 that is connected to the reference member 615 and is notparallel to the reference member 615 or the first member 611. In thisexample, first member 611 is shown as perpendicular to reference member615, but in other aspects of the invention (not shown) first member 611is not perpendicular to reference member 615. Dotted lines 621, 622 and623 represent contact paths of corresponding resistance probes assubstrate 650 is advanced along advancement direction 605 paststationary probes. The resistance probes can be independent from oneanother or can be contact elements of a probe unit 510 or 520 describedabove with reference to FIGS. 11A and 11B. For example, contact paths621, 622 and 623 can represent where contact elements 521, 522 and 523contact substrate 650 and first alignment structures 610. A highresistance value is measured between contact elements 521 and 522 unlessboth contact elements 521 and 522 are in contact with first alignmentstructure 610.

Reference member 615 of first alignment structure 610 has a length L₁that is sufficiently long that the corresponding resistance probe (forexample first contact element 521) will be in continuous contact with itas substrate 650 is advanced along advancement direction 605 in theregion where second and third contact elements 522 and 523 can come intocontact with first alignment structure 610. With reference to FIGS. 11Band 13A, suppose the substrate 650 is advanced relative to probe unit520 such that second contact element 522 and third contact element 523contact the leftmost edge of first member 611 first, and approximatelyat the same time t₀. Then as substrate 650 continues to be advanced,second contact element 522 and third contact element 523 contact therightmost edge of first member 611 a bit later at t₁ and approximatelyat the same time as each other. Then as substrate 650 continues to beadvanced, second contact element 522 contacts the leftmost edge ofsecond member 612 at t₂. Then as substrate 650 continues to be advanced,third contact element 523 contacts the leftmost edge of second member612 at t₃. At each of these edges a large change in the value of themeasured resistances occurs. When a second or third contact element 522or 523 enters the first or second member 611 or 612 of first alignmentstructure the corresponding value of resistance decreases dramatically.The exact resistance value is not of interest, only that it suddenlydecreases. Similarly when a second or third contact element 522 or 523exits the first or second member 611 or 612 of first alignment structure610, the resistance value increases dramatically. Location of theleftmost edge of first member 611, either by using a clock measurementof the timing of t₀ and a known value of the advancement speed, or bycorrelating the resistance value decrease with an encoder measurement oflocation of substrate 650, identifies the location of first alignmentstructure 610 along the X direction. A further refinement of thelocation of first alignment structure 610 along the X direction isobtained by measuring the sudden increase of resistance at the rightmostedge of second member 612 at t₁. The identification of both the leftmostedge and the rightmost edge of first member 611 determines the width offirst member 611 so that manufacturing variation in linewidth of firstmember 611 can be corrected for in determining the location of firstalignment structure 610 along the X direction.

Because second member 612 is not parallel to first member 611, thelocation of first alignment structure 610 along the Y direction can alsobe identified by determining the locations where second contact element522 exits first member 611 at t₁ and where second contact element 522enters second member 612 at t₂, thereby indicating the spacing S betweenthe first member 611 and the second member 612. As seen in FIG. 13A,spacing S varies along the Y direction as S=S₀+bY, where S₀ is thespacing between the first member 611 and the second member 612 wherethey intersect reference member 615 at Y₀, b is the rate of change ofspacing, and Y is measured with reference to Y₀. Therefore the Y₂position of the second contact element 522 is given by Y₂=(S₂−S₀)/b. Thecoefficient b for rate of change of spacing is known. The nominal valueof S₀ is known, and can be corrected for manufacturing error by thelinewidth measurement described above. Although it is not necessary thatthe first contact element 521 be targeted for the center of referencemember 615 along its width W₁, that is a preferred target. When firstalignment structure is positioned in preferred alignment relative toprobe unit 520, the center of reference member 615 along width W₁ is incontact with first contact element 521, and second contact element 522is spaced a known distance D₁ away (FIG. 11B). The preferred locationY_(2i) for second contact element 522 is given by Y_(2i)=D₁−W₁/2.Measurement of the actual spacing S₂=S₀+bY₂ is used to determine thealignment error ΔY between the actual position Y₂ of second contactelement 522 and the preferred position Y_(2i) of second contact element522 relative to first alignment structure 610. In particular, sinceY₂=(S₂−S₀)/b,ΔY=Y ₂ −Y _(2i)=(S ₂ −S ₀)/b−D ₁ +W ₁/2.

An additional determination of the Y offset of first alignment structure610 can be made in similar fashion using the resistance values measuredby third contact element 523 to determine spacing S₃ between therightmost edge of first member 611 and the leftmost edge of secondmember 612. The preferred location Y_(3i) for third contact element 523is given by Y_(3i)=D₁+D2−W₁/2. In addition to providing a secondmeasurement of ΔY alignment error for improved measurement accuracy, thethird contact element 523 can also provide an indication of skew, thatis, rotational misalignment of first alignment structure 610 relative toadvancement direction 605. Preferably, since first member 611 isperpendicular to reference member 615 in this example, and since probeunit 520 is aligned perpendicular to advancement direction 605, secondcontact element 522 and third contact element 523 should contact theleftmost edge of first member 611 at exactly the same time t₀. If thechanges in resistance value are not simultaneous, there is an indicationof skew.

It may not be practical, in some aspects of the invention, to have thelength L₂ of first member 611 be sufficiently long to permit a wideenough spacing D₂ of second contact element 522 and third contactelement 523 to provide a sufficiently accurate measurement of skew. Insuch aspects of the invention, a first probe unit 510 or 520 can belocated near first edge 656 of substrate 650 in order to take resistancemeasurements of first alignment structures 610, and a second probe unit510 or 520 can be located near the second edge 657 of substrate 650 inorder to take resistance measurements of second alignment structures616. The first and second alignment structures 610 and 616 can be formedsuch that if there is no rotational misalignment of pattern 654, theresistance measurements for the second members 522 will changesimultaneously for first and second alignment structures 610 and 616(assuming the two probe units near first edge 656 and second edge 657have been properly aligned relative to each other). Determination ofskew can be made by measuring differences with respect to simultaneouschanges.

The desired functioning of first alignment structure 610 provides someguidelines for its design, as well as for the design of the probecontact elements. Since it is assumed that first contact element 521will always hit reference member 615 as substrate 650 is moved alongadvancement direction 605 (nominally parallel to X), width W₁ ofreference member 615 along the Y direction should be sufficiently widethat if the maximum anticipated cross-track positioning error is ±Ealong the Y direction, width W₁ should be at least 2E. Because secondcontact element 522 should never hit reference member 615, even if firstcontact element is misaligned to be at the top of reference member 615,the distance D₁ between first contact element 521 and second contactelement 522 should be greater than W1. Because second contact element522 should be in a position to hit first member 611 even if firstcontact element 521 is misaligned to be at the bottom of referencemember 615, the length L₂ of first member 611 along a directionperpendicular to the X direction should be greater than width W₁ of thereference member 615 along the direction perpendicular to the Xdirection. In order to provide sufficient variation in spacing S betweenthe first member 611 and the second member 612, while also having thereference member 615 extending at least as long as the furthest apartportions of first member 611 and second member 612, it can beadvantageous for the length L₁ of reference member 615 along the Xdirection to be greater than the length L₂ of the first member 611 alongthe direction it extends.

As shown in FIGS. 12 and 13A, there can be a plurality of firstalignment structures 610 disposed near first edge 656 of substrate 650.In some aspects of the invention, the plurality of first alignmentstructures 610 can be distributed as one first alignment structure 610per piece of substrate 659 as in FIG. 12, where the pieces of substrate659 are bounded by separation lines 658. In other aspects of theinvention, there can be a plurality of first alignment structures 610near first edge 656 in a single piece as shown in FIG. 13A. By providinga plurality of first alignment structures 610 within a piece,registration can be monitored and corrections made within a piece. Thealignment structure 630 shown in FIG. 13B is related to the two firstalignment structures 610 in FIG. 13A in that the reference member 635has been lengthened along the X direction to enable resistancemeasurement of two pairs of members. Alignment structure 630 includesfirst member 631 that is connected to reference member 635 and extendsalong a second direction (Y in this example); second member 632 that isconnected to reference member 635 and is not parallel to referencemember 635 or first member 631; third member 633 that is parallel tofirst member 631; and fourth member 634 that is parallel to secondmember 632. Alignment structure 630 (or multiple copies of firstalignment structure 610 near first edge 656) can provide an alternativeway to measure skew where there is a probe unit only near first edge656. In particular, the amount of skew is measured by the difference inΔY alignment error for third member 633 and fourth member 634 minus theΔY alignment error for first member 631 and second member 632 divided bythe distance in X between the first member 631 and the third member 633.

In some aspects of the invention, reference member 615 or 635 can bepreformed on substrate 650. In these aspects, first member 611 or 631,second member 612 or 632, and any other members such as third member 633and fourth member 634 are formed at the same time as pattern 654. Ifpattern 654 is substantially transparent, at least first member (611 or631) and second member (612 or 632) will also be substantiallytransparent. In some aspects of the invention, preformed referencemember 615 or 635 is not substantially transparent, although it wouldstill be electrically conductive.

FIG. 14A shows another example of an alignment structure configurationthat can be used in a system where the relative motion of the substrate650 and the probe is in a single linear direction, such as advancementdirection 605. The alignment structure configuration includes a firstalignment bar 671 located near first edge 656 of substrate 650, a secondalignment bar 672 located near first alignment bar 671, and a thirdalignment bar 673 located near second edge 657 of substrate 650. Firstalignment bar 671 is tilted relative to advancement direction 605 suchthat it is not parallel to advancement direction 605. Second alignmentbar 672 is tilted relative to advancement direction 605 such that it isnot parallel to advancement direction 605 and also not parallel to firstalignment bar 671. Third alignment bar 673 is parallel to secondalignment bar 672. With reference to imaginary reference line 670extending along the Y direction, it can be seen that second alignmentbar 672 and third alignment bar 673 are separated along the Y direction,and have no offset relative to each other in the X direction. Firstalignment bar 671 is offset from second and third alignment bars 672 and673 in both X and Y. In addition, first alignment bar 671 has anopposite slope relative to second and third alignment bars 672 and 673.In this example, the X direction is parallel to advancement direction605, and the Y direction is parallel to the cross-track direction.

A first contact pair 661 including a first roller 662 and a secondroller 663 is positioned in line with first alignment bar 671, so thatas substrate 650 is advanced along advancement direction 605, firstroller 662 and second roller 663 will make contact with first alignmentbar 671. A second contact pair 664 including a first roller 665 and asecond roller 666 is positioned in line with second alignment bar 672,so that as substrate 650 is advanced along advancement direction 605,first roller 665 and second roller 666 will make contact with secondalignment bar 672 at a later time than the first contact pair 661 makescontact with the first alignment bar 671, due to the offset along Y ofthe second alignment bar 672. A third contact pair 667 including a firstroller 668 and a second roller 669 is positioned in line with thirdalignment bar 673, so that as substrate 650 is advanced alongadvancement direction 605, first roller 668 and second roller 669 willmake contact with third alignment bar 673 at about the same time thanthe second contact pair 664 makes contact with the second alignment bar672. In one aspect of the invention, all of the rollers in the contactpairs 661, 664 and 667 are conductive and are optionally mounted inpairs on insulating shafts 660.

A simplified diagram of first contact pair 661 and associated circuitryis shown in FIG. 14B. Connected between first roller 662 and secondroller 663 is a voltage V and a current measuring device I. As substrate650 is advanced along advancement direction 605, first and secondrollers 662 and 663 make contact with substrate 650 and first alignmentbar 671 as indicated by the dashed lines. Because of the slope of firstalignment bar 671, second roller 663 will first make contact with firstalignment bar 671 at second entry edge 676. As substrate 650 continuesto advance along advancement direction 605, first roller 662 next makescontact with first alignment bar 671 at first entry edge 675. Up to thispoint the current has been low but now makes a transition from low tohigh (as shown by current I₁ in FIG. 14C), thereby identifying theposition of first entry edge 675. Current stays high until second roller663 leaves first alignment bar 671 at second exit edge 678, resulting ina high to low transition (as shown by current I₁ in FIG. 14C), therebyidentifying the position of second exit edge 678. The spacing of firstand second rollers 662 and 663 and the geometry of first alignment bar671 are then used to determine the location of first alignment bar 671.Similarly, second contact pair 664 and third contact pair 667 aremonitored for current transitions as shown respectively by currents I₂and I₃ in FIG. 14C. Based on the speed of the substrate 650 alongadvancement direction 605 and the known amount X offset of the secondand third alignment bars 672 and 673, there will be a time intervalt_(a) between the current pulse in I₁ and the current pulse in I₂.Similarly there will be a time interval t_(b) between the current pulsein I₁ and the current pulse in I₂. If t_(a) and t_(b) are both equal tothe same predetermined time interval, then there is no alignment errorof substrate 650 along the Y cross track direction. Alignment errorsalong the cross track direction can be determined because the slopes ofthe second and third alignment bars 672 and 673 are different from theslope of the first alignment bar 671. With reference to FIG. 14A, ifsubstrate 650 is moved to the right in the Y direction, first contactpair 661 will make contact with first alignment bar 671 a bit later thannominal, and second contact pair 664 will make contact with secondalignment bar 672 a bit earlier than nominal. As a result, as shown inFIG. 14D, the time interval t_(a) will be shorter than the predeterminedtime interval shown in FIG. 14C. If the substrate had been moved to theleft, the time interval would be longer than the predetermined timeinterval (not shown). In FIG. 14D t_(a)=t_(b), so even though thesubstrate 650 is misaligned in Y, there is no skew error. Skew error isidentified when t_(a) does not equal t_(b) as in FIG. 14E.

In the examples described above, measurement of resistance has been donebetween two contact elements. It is known that two point resistancemeasurements are susceptible to error due to contact resistance, such asthat due to poor surface contact. FIG. 15A shows an example ofresistance measurements of alignment structures where two outer contactelements (first current contact 681 and second current contact 682) areused to provide current from a current source I_(S), and two voltagemeasurements are made at first voltage contact 683 and second voltagecontact 684 relative to a central reference contact 685. Optionally thefive contact elements 681-685 can be contained in a single probe unitsimilar to those of FIG. 11B or 14B. A continuous chevron alignmentstructure 680 having two legs 686 and 687, which are neither parallel toeach other nor to advancement direction 605, makes contact with contacts681-685 as the substrate (not shown) moves in advancement direction 605.Voltage transitions between first voltage contact 683 and referencecontact 685 and between second voltage contact 684 and reference contact685 indicate edges of continuous chevron alignment structure 680 insimilar fashion as described above.

FIG. 15B shows an example of resistance measurements on a split chevronalignment structure 690 having two legs 696 and 697, which are neitherparallel to each other nor to advancement direction 605. Four pointresistance measurements are made independently on each leg 696 and 697.For leg 696 current is provided by current source I_(S1) at outercontacts 691 and 694 and voltage V₁ is read across inner contacts 692and 693. Similarly current source I_(S1) is used to provide current toouter contacts 691 and 694 and voltage V2 is measured across innercontacts 692 and 693 for leg 697.

FIG. 16 shows a flowchart for a method for aligning a second pattern toa first pattern based on a first alignment structure having a locationidentified by measurements of an electrical characteristic according toan aspect of the invention. In Step 700, a first substrate having afirst pattern including the first alignment structure is provided. Thefirst alignment structure has a different magnitude of the electricalcharacteristic than the first substrate. In Step 710, an electricalprobe is used to measure the electrical characteristic corresponding toeach of a plurality of positions proximate the first substrate. In Step730 the measured electrical characteristic are compared as a function ofposition of the probe to identify a location of the first alignmentstructure. The location of the first alignment structure can beidentified by a difference between the measured electricalcharacteristic at a pair of the plurality of positions exceeding apredetermined threshold. The threshold can be set to any valueappropriate for detecting the location of the alignment structure. As anexample, the threshold can be set to be a difference of at least anorder of magnitude at a pair of a plurality of locations. In Step 730, asecond substrate having the second pattern including a second alignmentstructure is provided. In Step 740, the location of the second alignmentstructure is identified. In Step 750, the second substrate is aligned tothe first substrate using the identified locations of the first andsecond alignment structures.

In an aspect of the invention, Step 750 can further include thefollowing steps. A first reference feature is provided at a firstdistance and direction from the identified location of the firstalignment structure. A second reference feature is provided at seconddistance and direction from the identified location of the secondalignment feature. The first and second reference features are used toalign the second substrate to the first substrate. The first referencefeature can include a first hole in the first substrate, and the secondreference feature can include a second hole in the second substrate. Inthis example, the first and second reference features are used to alignthe second substrate to the first substrate by inserting a pin throughboth the first hole in the first substrate and the second hole in thesecond substrate. The predetermined distance can be set to any value,including zero.

In some aspects of the invention, the first alignment structure issubstantially transparent but the second alignment structure isnon-transparent. In these aspects, the location of the non-transparentsecond alignment structure can be optically identified. In anotheraspect of the invention, the method for aligning the patterns canfurther include a plurality of first substantially transparent patternson the first substrate, each of the plurality of first substantiallytransparent patterns including at least one first alignment structurehaving associated therewith a magnitude of the electrical characteristicthat is different from a magnitude of the electrical characteristic ofthe first substrate. The probe is used to measure the electricalcharacteristic at a plurality of locations to identify locations of eachof the first alignment structures associated with each of the pluralityof first substantially transparent patterns. The first substrate isdivided into a plurality of substrate pieces using the identifiedlocations of each of the first alignment structures such that each ofthe plurality of substrate pieces includes one of the plurality of firstsubstantially transparent patterns.

In various aspects of the invention, the electrical characteristic canbe resistance or capacitance. In an aspect of the invention, identifyingthe location of the first alignment structure includes identifying atleast one position along a first edge of the first alignment structureand at least one position along a second edge of the first alignmentstructure. The first edge can be disposed on a first side of a firstmember of the alignment structure and the second edge can be disposed ona second side of the first member of the alignment structure. In otheraspects of the invention, the first edge can be disposed on a firstmember of the alignment structure, and the second edge can be disposedon a second member of the alignment structure.

In some aspects of the invention, the electrical probe can be moved tomeasure the electrical characteristic corresponding to each of theplurality of positions proximate the first substrate. In these aspectsof the invention, the electrical probe includes a probe unit having afirst contact element, a second contact element, and a third contactelement that are electrically insulated from each other and arrayed innonlinear fashion. The probe unit is moved in a first direction untilthe electrical characteristic measured between the first contact elementand the second contact element differs by a first amount exceeding thepredetermined threshold to identify a first edge of the first alignmentstructure. The probe unit can then be moved in a second direction, notparallel to the first direction, until the electrical characteristicmeasured between the first contact element and the third contact elementdiffers by a second amount exceeding the predetermined threshold toidentify a second edge of the first alignment structure. The seconddirection can be perpendicular to the first direction.

In other aspects of the invention, the first substrate can be movedrelative to the electrical probe to measure the electricalcharacteristic corresponding to each of the plurality of positionsproximate the first substrate.

A system for aligning a second pattern to a first pattern based on afirst alignment structure having a location identified by measurementsof an electrical, according to an aspect of the invention, can compriseof

(i) a first substrate having the first pattern including the firstalignment structure, wherein the first alignment structure has adifferent magnitude of the electrical characteristic than the firstsubstrate.

(ii) an electrical probe.

(iii) a controller for controlling the relative position of theelectrical probe with respect to the first substrate to measure theelectrical characteristic corresponding to each of a plurality ofpositions proximate the first substrate, for comparing the measuredelectrical characteristic as a function of position of the probe toidentify the location of the first alignment structure by identifying adifference between the measured electrical characteristic at a pair ofthe plurality of positions exceeding a predetermined threshold.

(iv) a second substrate having the second pattern including a secondalignment structure formed thereon.

(v) a controller for identifying the location of the second alignmentstructure. This controller can be the same controller as in element(iii) or a different controller.

(vi) a registration mechanism for aligning the second substrate to thefirst substrate using the identified locations of the first and secondalignment structures.

The system can also include a support for the first substrate, thesupport including a hold-down mechanism for the first substrate. Thesystem can also include movers for moving the probe. A first mover canbe provided for moving the probe along a first direction that isparallel to the support for the first substrate or the first substrate.In this aspect of the invention, a controller can be configured tocontrol the probe to take a first measurement at a first position, movethe probe to a second position that is a first distance along the firstdirection, and take a second measurement at the second position. Inanother aspect of the invention, the controller can be furtherconfigured to control the probe to move the probe to a third positionthat is a second distance along the first direction and take a thirdmeasurement at the third position, wherein the second distance is lessthan the first distance if the second measurement corresponds to aproximity of the first alignment structure. Alternately, the controllercan be further configured to control the probe to move the probe to athird position that is a second distance along a direction opposite thefirst direction and take a third measurement at the third position,wherein second distance is less than the first distance. The system canalso include a second mover for moving the probe along a seconddirection that is parallel to the support for the first substrate or thefirst substrate and not parallel to the first direction. A third movercan move the probe along a third direction that is perpendicular to thesupport for the first substrate or the first substrate to move the probeinto and out of contact with the first substrate.

In various aspects of the invention, the probe can be a resistance probeor a capacitance probe. The system is not limited to a single probe butcan have alternate arrangements including multiple probes. In someaspects of the invention, the movers move the support for the firstsubstrate or the first substrate, rather than the probe. For example,the first mover can move the support for the first substrate or thefirst substrate along a first direction that is parallel to the supportfor the substrate. The second mover can move the support for the firstsubstrate or the first substrate along a second direction that isparallel to the support for the first substrate or the first substrateand not parallel to the first direction.

In some aspects of the invention, the registration mechanism can includea marking station for providing at least one reference mark on the firstsubstrate at a distance and direction, determined by the controller,from the identified location of the first alignment structure. Themarking station includes at least one of an ink marker, a laser, a bladea drill, a heated tip, an indenter or a hole punch to make the referencemark. The registration mechanism can further include a positioner forpositioning a second substrate on which the second pattern is formedrelative to the first substrate such that the pattern is alignedrelative to the first alignment structure on the first substrate.

FIG. 17 shows a flowchart for a method for forming a second pattern inregistration with a first pattern on a substrate, according to an aspectof the invention. In Step 800, a first substrate, having an associatedfirst magnitude of an electrical characteristic, and a first pattern ona surface of the first substrate, the first pattern including at leastone alignment structure that is associated with a second magnitude ofthe electrical characteristic that is different from the first magnitudeof the electrical characteristic of the substrate, is provided. In Step810, an electrical probe is used to measure the electricalcharacteristic corresponding to each of a plurality of positionsproximate the substrate, wherein the measured electrical characteristiccorresponds to the alignment structure when the probe is proximate tothe alignment structure, and the measured electrical characteristiccorresponds to the substrate when the probe is not proximate to thealignment structure. In Step 820, a controller is used to interpret themeasured electrical characteristics for identifying a location of thealignment structure. In Step 830, the identified location of thealignment structure is used to control the forming of the second patternsuch that it is in registration with the first pattern. The substratecan be moved proximate the probe along a predetermined direction.

In an aspect of the invention, moving the substrate further includesusing an advancement mechanism to feed the substrate from a supply roll,past the stationary probe, and toward a take-up roll. The first patternis formed on the surface of the substrate at a pattern forming stationlocated between the supply roll and the stationary probe. A curingstation can be located between the pattern forming station and thestationary probe. In another aspect of the invention, there can be a gapbetween the surface of the substrate and the probe.

The probe for measuring capacitance can include elements disposed onopposite sides of the substrate. The probe for measuring resistance canbe configured to contact the surface of the substrate. The probe caninclude a rounded contact surface or a rotatable contact surface. Theprobe can also include a plurality of contact members that areelectrically insulated from each other.

In various aspects of the invention, the second pattern is formed on asame surface of the substrate as the first pattern. In other aspects ofthe invention, the first pattern is formed on a first surface of thesubstrate, and the second pattern is formed on a second surface that ison the opposite side of the substrate from the first surface. The firstpattern, the alignment structure, the second pattern, or the substratecan be substantially transparent.

In an aspect of the invention, a system for forming a second pattern inregistration with an alignment structure of a first pattern on asubstrate comprises:

(i) an advancing mechanism for moving the substrate.

(ii) a stationary probe for measuring an electrical characteristic at aplurality of positions proximate the moving substrate.

(iii) a controller for interpreting the measured electricalcharacteristic as a function of position for identifying a location ofthe alignment structure.

(iv) a patterning station for forming the second pattern on a surface ofthe substrate in registration with the first pattern based on theidentified location of the alignment structure.

The advancing mechanism can include movers for moving the substrate pastthe stationary probe along a first direction and a second directiondifferent from the first direction.

In another aspect of the invention, a system for determining analignment location associated with a pattern formed on a substrate bymaking electrical measurements as the substrate is moved along anadvancement direction comprises:

(i) an alignment structure formed on the substrate, the alignmentstructure having a first member extending along a first direction thatis not parallel to the advancement direction and a second memberextending along a second direction that is not parallel to either theadvancement direction or to the first member, wherein the first memberand the second member are electrically conductive and substantiallytransparent.

(ii) one or more probes responsive to relative motion between thesubstrate and the probe to identify particular portions of the first andsecond members of the alignment structure and produce signalsidentifying such portions.

(iii) a controller responsive to signals produced by the probe todetermine an alignment location associated with the pattern formed onthe substrate.

In some aspects of the invention, the alignment structure can furtherinclude a reference member extending along a direction parallel to theadvancement direction and intersecting both the first and secondmembers. Each of the first member and second members of the alignmentstructure has a light transmittance, preferably, between 80% and 100%.Further, each of the first and second members of the alignment structurehas a resistivity, preferably, between 10⁻⁸ ohm-meter and 1 ohm-meter.In some aspects of the invention, each of the first and second membersof the alignment structure has an electrical resistance that is lessthan one percent of an electrical resistance of the substrate asmeasured by two contacts that are positioned a predetermined distanceapart.

In various aspects of the invention, the members of the alignmentstructure can include an inorganic oxide film or an organic film. Theinorganic oxide film can be include poly(3,4-ethylenedioxythiophene),grapheme, orcarbon nanotubes.

The invention has been described in detail with particular reference tocertain preferred aspects of the invention, but it will be understoodthat variations and modifications can be effected within the spirit andscope of the invention. And even though specific aspects of theinvention have been described herein, it should be noted that theapplication is not limited to these aspects of the invention. Inparticular, any features described with respect to one aspect may alsobe used in other aspects of the invention, where compatible. And thefeatures of the different aspects of the invention may be exchanged,where compatible.

PARTS LIST

-   10 mask aligner-   15 camera-   20 exposure station-   25 radiation-   30 first mask-   32 first pattern-   34 boxes-   35 alignment mark-   36 alignment mark-   40 second mask-   42 second pattern-   44 circles-   45 alignment mark-   46 alignment mark-   50 substrate-   52 pattern-   54 boxes-   55 alignment mark-   56 alignment mark-   58 photoresist-   62 pattern-   64 boxes-   65 alignment mark-   66 alignment mark-   100 system-   110 support-   112 mechanical registration feature-   114 vacuum holes-   120 controller-   122 measurement module-   124 registration module-   126 mover control module-   131 first probe-   132 probe tip-   133 second probe-   134 probe tip-   135 capacitance probe-   136 plate-   137 plate-   141 first mover-   142 second mover-   143 third mover-   150 first substrate-   151 side of first substrate-   152 first alignment structure-   153 opposite side of first substrate-   154 first pattern-   156 edge-   158 separation line-   159 substrate piece-   160 marking station-   162 marking element-   164 reference mark-   170 contact position-   171 first position-   172 second position-   173 third position-   176 first position-   177 second position-   178 third position-   180 positioner-   190 pin-   191 first mover-   192 second mover-   195 camera-   200 pattern forming station-   210 pattern forming station-   220 probe unit-   221 first contact element-   222 second contact element-   223 third contact element-   225 contact surface-   226 alignment structure-   227 first edge-   228 adjacent edge-   250 second substrate-   252 second alignment structure-   254 second pattern-   264 reference mark-   300 flexographic printing system-   302 supply roll-   304 take-up roll-   305 roll-to-roll direction-   306 roller-   307 roller-   310 print module-   311 plate cylinder-   312 printing plate-   313 raised features-   314 impression cylinder-   315 anilox roller-   316 curing station-   317 probe-   318 controller-   319 roller-   320 print module-   321 plate cylinder-   322 printing plate-   324 impression cylinder-   325 anilox roller-   326 curing station-   327 probe-   328 controller-   329 roller-   330 print module-   331 plate cylinder-   332 printing plate-   334 impression cylinder-   335 anilox roller-   336 curing station-   337 probe-   338 controller-   339 roller-   340 print module-   341 plate cylinder-   342 printing plate-   344 impression cylinder-   345 anilox roller-   346 curing station-   348 controller-   350 substrate-   351 first side-   352 second side-   400 printing system-   401 first pattern forming station-   402 second pattern forming station-   405 advancement direction-   410 drive roller-   411 roller-   412 roller-   450 substrate-   452 first alignment structure-   454 first pattern-   455 another first alignment structure-   456 first edge-   457 second edge-   458 separation line-   459 frame-   461 first stationary probe-   462 second stationary probe-   463 first controller-   464 second controller-   472 second alignment structure-   474 second pattern-   475 another second alignment structure-   510 probe unit-   511 contact element-   512 contact element-   515 contact surface-   520 probe unit-   521 first contact element-   522 second contact element-   523 third contact element-   605 advancement direction-   610 first alignment structure-   611 first member-   612 second member-   615 reference member-   616 second alignment structure-   621 contact path-   622 contact path-   623 contact path-   630 alignment structure-   631 first member-   632 second member-   633 third member-   634 fourth member-   635 reference member-   650 substrate-   654 pattern-   656 first edge-   657 second edge-   658 separation line-   659 substrate piece-   660 shaft-   661 first contact pair-   662 first roller-   663 second roller-   664 second contact pair-   665 first roller-   666 second roller-   667 third contact pair-   668 first roller-   669 second roller-   670 reference line-   671 first alignment bar-   672 second alignment bar-   673 third alignment bar-   675 first entry edge-   676 second entry edge-   677 first exit edge-   678 second exit edge-   680 contiguous chevron alignment structure-   681 first current contact-   682 second current contact-   683 first voltage contact-   684 second voltage contact-   685 reference contact-   686 leg-   687 leg-   690 split chevron alignment structure-   691 outer contact-   692 inner contact-   693 inner contact-   694 outer contact-   696 leg-   697 leg-   700 Step of providing a first substrate-   710 Step of using a probe to measure an electrical characteristic at    a plurality of locations proximate the first substrate-   720 Step of identifying a location of a first alignment structure-   730 Step of providing a second substrate-   740 Step of identifying a location of a second alignment structure-   750 Step of aligning the first and second substrates using the    locations of the first and second alignment structures-   800 Step of providing a first substrate and a first pattern having    an associated alignment structure on the first substrate-   810 Step of using a probe to measure an electrical characteristic at    a plurality of locations proximate the first substrate-   820 Step of identifying a location of the first alignment structure-   830 Step of forming a second pattern on the first substrate in    registration with the first pattern

The invention claimed is:
 1. A method for forming a second pattern inregistration with a first pattern on a substrate, comprising: providingthe substrate, the substrate having a first magnitude of an electricalcharacteristic associated therewith, the substrate also having a firstpattern on a surface of the substrate, the first pattern including atleast one alignment structure that is associated with a second magnitudeof the electrical characteristic that is different from the firstmagnitude of the electrical characteristic of the substrate; using acontroller to control an electrical probe to measure the electricalcharacteristics of the substrate and of the alignment structurecorresponding to each of a plurality of positions at or near thealignment structure, wherein the measured electrical characteristiccorresponds to the alignment structure when the electrical probe isproximate to the alignment structure, and the measured electricalcharacteristic corresponds to the substrate when the electrical probe isnot proximate to the alignment structure; using a controller tointerpret the measured electrical characteristics for identifying alocation of the alignment structure; and using a controller, responsiveto the identified location of the alignment structure, to control theforming of the second pattern so that it is in registration with thefirst pattern.
 2. The method of claim 1, further including moving thesubstrate proximate the electrical probe along a predetermineddirection.
 3. The method of claim 2, wherein the electrical probe beingstationary in a fixed position, moving the substrate further includesfeeding the substrate from a supply roll past the stationary electricalprobe toward a take-up roll.
 4. The method of claim 3, wherein the firstpattern is formed on the surface of the substrate at a pattern formingstation located between the supply roll and the stationary electricalprobe.
 5. The method of claim 4, wherein a curing station is locatedbetween the pattern forming station and the stationary electrical probe.6. The method of claim 1, wherein using the electrical probe to measurethe electrical characteristic corresponding to each of the plurality ofpositions at or near the alignment structure further includes providinga gap between the surface of the substrate and the electrical probe. 7.The method of claim 6, wherein the electrical characteristic iscapacitance.
 8. The method of claim 7, wherein the electrical probe formeasuring capacitance includes elements disposed on opposite sides ofthe substrate.
 9. The method of claim 1, wherein the electricalcharacteristic is resistance.
 10. The method of claim 9, wherein theelectrical probe is configured to contact the surface of the substrate.11. The method of claim 10, wherein the electrical probe includes atleast one rounded contact surface.
 12. The method of claim 10, whereinthe electrical probe includes at least one rotatable contact surface.13. The method of claim 1, wherein the electrical probe includes a firstcontact member and a second contact member that is electricallyinsulated from the first contact member.
 14. The method of claim 1,wherein the second pattern is formed on a same surface of the substrateas the first pattern.
 15. The method of claim 1, wherein the firstpattern is formed on a first surface of the substrate, and wherein thesecond pattern is formed on a second surface that is on the oppositeside of the substrate from the first surface.
 16. The method of claim 1,wherein the first pattern and the alignment structure are substantiallytransparent.
 17. The method of claim 16, wherein the second pattern issubstantially transparent.
 18. The method of claim 1, wherein thesubstrate is substantially transparent.
 19. The method of claim 1,wherein using the electrical probe to measure the electricalcharacteristic corresponding to each of the plurality of positions at ornear the alignment structure further includes moving the electricalprobe.
 20. The method of claim 19, wherein moving the electrical probefurther includes: providing a probe unit including a first contactelement, a second contact element, and a third contact element that areelectrically insulated from each other and arrayed in nonlinear fashion;moving the probe unit in a first direction until the electricalcharacteristic measured between the first contact element and the secondcontact element differs by a first amount exceeding the predeterminedthreshold to identify a first edge of the alignment structure; andmoving the probe unit in a second direction nonparallel to the firstdirection until the electrical characteristic measured between the firstcontact element and the third contact element differs by a second amountexceeding the predetermined threshold to identify a second edge of thefirst alignment structure.